1. Field of the Invention
The present invention relates generally to novel compositions comprising (a) controlled distribution block copolymers of mono alkenyl arenes and conjugated dienes having the general formula A-EB/A-A and (A-EB/A)nX, and (b) thermoplastic polyurethane elastomers that result in surprising improvements in properties for the composition.
2. Background of the Prior Art
Thermoplastic urethane (“TPU”) elastomers are an important class of materials in the rapidly growing field of thermoplastic elastomers. TPUs are generally made from long chain diols, chain extenders and polyisocyanates. The properties are achieved by phase separation of soft and hard segments. The hard segment, formed by, for example, adding butanediol to the diisocyanate, provides mechanical strength and high temperature performance. The soft segment, consisting of long flexible polyether or polyester chains with molecular weight of 600 to 4000, controls low temperature properties, solvent resistance and weather resistance.
Urethane based thermoplastic elastomers have an impressive range of performance characteristics such as outstanding scratch/abrasion resistance, excellent oil resistance and high tensile/tear strength. TPU can be processed by injection molding, blown film, extrusion, blow molding and calendaring. It is used in a broad range of applications such as films and sheets, athletic equipment, hoses/tubing, medical devices and automotive molded parts. However, application of TPU is limited when low hardness (<70 A) is required, such as applications when soft touch is required. It is difficult to produce soft grade TPU materials without adding plasticizers, which are not desirable in some applications.
Others have proposed various blends of TPU with other polymers. U.S. Pat. No. 3,272,890 discloses blends of 15 to 25 weight percent of polyurethane in polyethylene. This is achieved by first melting and fluxing the polyethylene in a Banbury mixer to which is added the polyurethane. In a series of U.S. Pat. Nos. 3,310,604; 3,351,676; and 3,358,052, there is disclosed polyurethanes having dispersed therein 0.2 to 5 weight percent polyethylene. U.S. Pat. No. 3,929,928 teaches that blends of 80:20 to 20:80 weight ratio of chlorinated polyethylenes with polyurethanes and containing 1 to 10 pph of polyethylene result in improved processability, particularly in the manufacture of films or sheets by milling or calendering. Such blends are more economical than the polyurethane alone.
U.S. Pat. Nos. 4,410,595 and 4,423,185 disclose soft resinous compositions containing 5 to 70 weight percent thermoplastic polyurethanes and 30 to 95 percent of polyolefins modified with functional groups such as carboxyl, carboxylic acid anhydride, carboxylate salt, hydroxyl, and epoxy. One of the features of the disclosed blends is their adhesion to other polymeric substances such as polyvinyl chloride, acrylic resins, polystyrenes, polyacrylonitriles, and the like. This property leads to their prime utility in the coextrusion, extrusion coating, extrusion laminating, and the like of polymer laminates. U.S. Pat. No. 4,883,837 discloses thermoplastic compatible compositions comprising (A) a polyolefin, (B) a thermoplastic polyurethane, and a compatibilizing amount of (C) at least one modified polyolefin. U.S. Pat. No. 4,088,627 discloses multicomponent blends of thermoplastic polyurethane, a selectively hydrogenated styrene/diene block copolymer and at least one dissimilar engineering thermoplastic. U.S. Pat. No. 7,030,189 discloses blends of a thermoplastic polyurethane, a polar group-containing thermoplastic elastomer and another thermoplastic elastomer.
However, none of these blend compositions results in the desired soft touch, along with excellent clarity. What is needed is a compound containing TPU that has the proper hardness and the desired clarity.